Only a fortnight ago he was representing the family of a child recovering from severe illness who were challenging the Stomont education minister's decision not to immediately close schools amid the escalating coronavirus crisis.

KRW Law has encouraged people to send Mr Murphy and his family messages of support.

Kevin Winters, on behalf of the Belfast-based firm, said the response had been "humbling and inspiring".

Niall Murphy with Irish News columnist Brian Feeney at the launch of the Ireland's Future initiative at Malone Lodge Hotel in Belfast. Picture by Mal McCann

"Niall's condition has not altered significantly at present," he told PA.

"His family and colleagues in KRW Law have been overwhelmed with the outpouring of support from the public, not just in Ireland but across the globe.

"The loyalty shown to him in his hour of need has been humbling and inspiring.

"The multitude of messages received from the legal profession, clients and so many other well-wishers will give much-needed comfort and support to his family at this very difficult time."

Among Mr Murphy's recent clients were Trevor Birney and Barry McCaffrey, the journalists behind the award-winning film No Stone Unturned about the UVF's massacre at the Heights Bar in Loughinisland in 1994.

The solicitor represented them in a successful legal challenge against police search warrants over whistleblower material.

Mr Birney said on Twitter: "Niall Murphy has Covid-19. He supported my family who know him simply as 'uncle Murph' – he's a true gentleman as well as a tenacious and brilliant lawyer.

"He needs your support as he faces the toughest battle of his life."

Mr Murphy is a representative of Ireland's Future, a civic nationalism group aiming to promote discussion about a united Ireland in the context of Brexit.

He is also a member of the board of directors for the campaign group Relatives for Justice.

The group said: "Niall Murphy is a husband, father, son, brother, friend, lawyer, sportsman, Irishman and an inspiration.

"He is also a valued member of the board of directors of Relatives for Justice. He has fought for and alongside many families seeking truth, justice and acknowledgement."

Antrim GAA was among the hundreds who posted messages of support online for Mr Murphy, a 2002 All-Ireland winning Antrim junior hurler.

It tweeted: "Prayers are with Niall and family at this time. Keep fighting Niall – the Saffrons need you!"

Stephen Jennings, chairman of St Enda's GAA club, said that Mr Murphy "lives for his family, the club and our culture".

He said on Facebook: "I know that big Naomh Éanna heart will pull him through this tough time.

"He never held back on the field and he will not hold back in this battle."

Sinn Féin North Belfast MP John Finucane described him as "my good friend as well as a fellow Gael and solicitor", while SDLP leader Colum Eastwood said: "Solidarity with Niall Murphy and his family."

Niall Murphy with John Finucane and investigative journalists Barry McCaffrey and Trevor Birney in 2018. Picture by Liam McBurney/PA